Sun Java System Message Queue 4.3 Developer's Guide for C Clients

Receiving a Message Synchronously

If you have created a synchronous consumer, you can use one of three receive functions: MQReceiveMessageNoWait, MQReceiveMessageWait , or MQReceiveMessagewithTimeOut. In order to use any of these functions, you must have specified MQ_SESSION_SYNC_RECEIVE for the receive mode when you created the session.

When you create a session you must specify one of several acknowledge modes for that session. If you specify MQ_CLIENT_ACKNOWLEDGE as the acknowledge mode for the session, you must explicitly call the MQAcknowledgeMessages function to acknowledge messages that you have received. If the session is transacted, the acknowledge mode parameter is ignored.

When the receiving function returns, it gives you a handle to the delivered message. You can pass that handle to the functions described in Processing a Message, in order to read message properties and information stored in the header and body of the message.

It is possible that a message can be lost for synchronous consumers in a session using AUTO_ACKNOWLEDGE mode if the provider fails. To prevent this possibility, you should either use a transacted session or a session in CLIENT_ACKNOWLEDGE mode.

Because distributed applications involve greater processing time, such an application might not behave as expected if it were run locally. For example, calling the MQReceiveMessageNoWait function might return MQ_NO_MESSAGE even when there is a message available to be retrieved on the broker. See the usage notes provided in the section MQReceiveMessageNoWait for more information.